The invention relates to a composition which is polymerizable by ring-opening metathesis polymerization (ROMP) comprising at least one monomer that is polymerizable by ROMP, at least one initiator of the Hoveyda-Grubbs type for initiating the ROMP and at least one retarder selected from the group consisting of heterocyclic amines having a ring with at least one N-atom and five or less atoms constituting the ring bearing the at least one N-atom. The invention further relates to a process for the preparation of a composition which is polymerizable by ROMP, a dental material obtainable by polymerizing a composition according to the invention and the use of a substance selected from the group consisting of heterocyclic amines having a ring with at least one N-atom and five or less atoms constituting the ring bearing the at least one N-atom or of a mixture of two or more of such substances as a retarder in ROMP.
Addition polymerizing reactions have been widely used in the field of dental applications. Mostly silicon resins have been utilized and have been cured, often as a two-part system via hydrosilylation reaction. An advantage of such systems is their flexible working time which, depending on the requirements, can be adjusted broadly within a range of from less than about one minute up to several hours. The working time can generally be controlled via the components present in the composition to be polymerized or by specifically adding retarders or inhibitors to the catalyst component.
Due to reasons which have, e.g., been mentioned in the prior art (see, e.g., U.S. Pat. No. 6,844,409 B2) addition polymerizable systems have many shortcomings. In order to remedy some of those shortcomings, another type of polymerization system has been developed where curing is achieved by a ring-opening metathesis polymerization (ROMP).
According to a definition given in U.S. Pat. No. 6,844,409 B2, metathesis is often understood to mean the metal catalyzed redistribution of carbon-carbon double bonds. A ROMP polymerizable composition generally can comprise a resin system that includes functionalities or groups that are curable by ROMP together with a metathesis catalyst such as a Ruthenium carbene complex.
U.S. Pat. No. 6,844,409 B2 relates to a composition curable by metathesis reaction comprising an olefin-containing resin system and metathesis catalyst. The metathesis is initiated by a Ruthenium carbene complex catalyst which is increased in activity by either an activity enhancing ligand or by incorporation of a catalyst accelerator into the described resin formulation. As catalyst accelerators sulfosuccinate salts are described. Retardation of the ROMP-reaction is not mentioned in the document.
Slugovc, Demel and Stelzer describe in ChemCommun 2002, 2572-2573 the influence of N-substituted compounds on ROMP polymerization with a so-called super-Grubbs catalyst. The use of functional group bearing additives in large amounts and the influence of such additives on the polymerization behaviour is described. While generally effects of slowing down the polymerization and a large influence on the polymer properties is described, neither a tailored retardation of the polymerization reaction or the absence of a significant influence on the mechanical properties of the obtained polymer are described in the document.
Matos and Lima-Neto Journal of molecular catalysis A: chemical 222 (2004) 81-85 describe the formation of a ruthenium complex which quantitatively polymerizes norbornene via ROMP in less than one minute at RT. While a decrease of catalyst activity upon the addition of ethyldiazoacetate is observed, the phenomenon of retardation, leaving the general polymerization mechanism basically unchanged is not described in the document.
US 2004/0225073 A1 describes a composition curable by a metathesis reaction upon mixing its components, which comprises an olefin-containing substrate, a metathesis catalyst and a reaction control agent for doing the progress of the metathesis reaction. The reaction control agent is an organic compound that contains carbon-carbon double and/or triple bonds and one or more Group 14 atoms and is present in an amount effective to slow the progress of the metathesis reaction. The document also describes the use of pyridine, triethylamin and benzotriazole as comparative retarders.
Upon comparing the retardation properties of these compounds, the document comes to the conclusion that they either accelerate the curing process (triethylamin), suppress the curing reaction (benzotriazole) or have no effect at all (pyridine).
US 2002/0153096 A1 relates to an adhesion agent composition comprising at least one olefin compound having at least one metathesis active double bond, wherein the olefin is substituted or unsubstituted and at least one compatibilising functionality for interacting with the substrate surface. A retarder which does not become part of the polymer is not mentioned in the document.
U.S. Pat. No. 6,001,909 relates to a composition comprising at least one tight cyclo olefin, a catalyst for the ring opening metathesis polymerization, a filler and a silane. The silanes are added in order to increase toughness, heat stability and dielectric loss factor of ROMP-polymerized systems. The silanes can carry substituents and are used in an amount of from 0.01 to 20% by weight in relation to the weight to the composition. Curing is achieved by heating the sample for 2 hours to 80° C., 4 hours to 100° C. and 1 hour to 150° C.
Yakov S. Vygodskii et al deal with the scope and limitations of Ring-Opening Metathesis Polymerization (ROMP) in ionic liquids (Macromolecules 2006, 39, 7821-7830).
US 2006/0241257 A1 describes metathesis-curable composition with a reaction control agent. In the examples tetra allyl silane (TAS) is used as reaction control agent.
Due to the shortcomings of the systems described in the prior art, there was a need for improved compositions which are curable by ROMP, especially for compositions which can be used in the dental field.